Engineering Plastic Nanoparticles for Super-Resolution Tracking of Lipid Membrane Interactions

Abstract

Single-particle measurements are essential for understanding the complex and often subtle interactions of engineered nanoparticles with biological systems. However, the preparation of plastic nanoparticles (PNP) for single-particle experiments has been hindered by challenges in reproducibility and fluorescence functionality. Here, we use a robust and simple method for preparing fluorescently labeled PNPs using confined impingement jets with dilution (CIJ-D) mixer. We prepared PNPs from individual polystyrene (PS), polypropylene (PP), polyvinyl chloride (PVC), and polylactic acid (PLA) powders with a narrow particle size distribution (between 50-100 nm) and incorporated Nile Red (NR) dye into these particles. These PNPs exhibit colloidal stability, uniform fluorescence intensity, and compatibility with single particle tracking measurements. To demonstrate the applicability of our approach, we tracked the interactions of individual PNPs with lipid bilayer surfaces composed of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) and cholesterol. Using super-resolution diffusion analysis (fluorescence correlation spectroscopy super-resolution optical fluctuation; fcsSOFI), we characterized the nanoscale diffusion and interaction dynamics of PNPs on the lipid bilayer surface. While electrostatic interactions play a major role in PNP transport dynamics on the bilayer, cholesterol induces slower surface diffusion. Our method provides an easy solution to prepare model PNP systems and study the PNP-membrane interactions using single-particle fluorescence microscopy.